Ceramic Matric Composite (CMC) materials are formed from ceramic fibres 10 reinforcing a ceramic matrix an example being shown in FIG. 1. CMC materials have excellent high temperature mechanical properties. CMC materials are currently being considered to replace high temperature metal alloys (such as nickel based superalloys) in applications such as gas turbine engine segments, vanes and blades, and also in combustor heat shields.
CMC materials need machining processes such as grinding, drilling or milling to achieve the final shape of the workpiece. Conventional drilling cutter geometries were designed several decades ago and have been optimised for the machining of homogenous materials. For example, in the majority of drill bits, the cutting lips are the only cutting regions. The heterogenic, anisotropic and high hardness properties of these CMC materials means that conventional cutting tools have low material removal rates, a short working life and poor machined surface quality.
Conventional cutting tools experience high wear rates, particularly when the cutting force is dynamically varying through the cut (as is the case for CMC materials). Therefore the cutting edge geometry is rapidly changed, so decreasing significantly the resulting surface quality. This is further exaggerated when machining small tight tolerance features such as micro-size holes and grooves.